The number 6 has a special significance. It represents the Law and Order and also associated with a Karmic Law of cause and effect. Number 6 is a perfect number, symmetrical in all parts, the number of the Soul.
Plums are ready they are not hard as a rock, soft just a little when pressed. I wouldn't use windfall, they are too ripe. If your making jam, it is best to use some underripe with the ripe ones. Last season I added small diced candied ginger to the plum jam. Really turned out nice.
When planting the fresh plum seeds, they should be 3 inches deep in the soil. Mark where you have planted the pit so you can find it in the spring. Leave the plum pit outside through the winter months and watch for any sprouting; thereafter, keep the new plant moist and watch it grow.